Machine for intraoperative radiation therapy

ABSTRACT

A machine for intraoperative radiation therapy or IORT (Intra Operative Radio Therapy), includes a mobile body, having at least two driving wheels and at least an idle wheel, each driving wheel being operated by a corresponding moving engine, the machine including a radiating head connected to the body, for emitting an electron beam, handling elements which are integral with the radiating head, engine unit for moving the radiating head, for impressing to the radiating head at least a vertical translation motion. The handling elements include at least three bidirectional sensors, for measuring both a traction stress and a compression stress, each of which sends to a control processor an electric signal proportional to a measured stress which is orthogonal to the sensor. The control processor operates the moving engines of each driving wheel and the engine unit proportionally to the stresses measured by the at least three bidirectional sensors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of copending U.S. application Ser. No.10/515,991, which is the national stage of international applicationPCT/IT/03/00336 filed on May 29, 2003, which claims foreign priority toItalian application No. RM 2002 A000301 filed May 31, 2002. The entirecontents of each of these applications is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention concerns a machine for intraoperative radiationtherapy or IORT (Intra Operative Radio Therapy) which is easily movable,having reduced weight and size, and which makes possible, in a reliable,simple and efficient way, to radiate an electron beam drasticallyreducing the diffusion of X rays, accurately controlling environmentalradiation, and very precisely measuring the radiation dose.

BACKGROUND OF THE INVENTION

It is known that Intraoperative Radiotherapy consists in treating thepatient with ionising radiations in the course of the surgicaloperation. IORT, initially developed by some, mainly Japanese and US,research institutes, since sixties to eighties, began to ripen in thefollowing decade, with the creation of a specific international society,the ISIORT, and increasingly participated biennial meetings methodicallyfollowing one another.

However, in mid-nineties the conviction spread among the experts thatIORT would have remained prerogative of large university centres whichcould face the big logistical costs that IORT involved. In fact, out ofthe institutions dedicated to research, it could not be proposed toinvest considerable amounts of money for a therapy that, due to limitedFigures, could not produce statistically reliable data. Hence, IORTremained a branch of excellence performed by researchers who tried tofind a standardisation in order to have data which were comparable andtherefore apt to be added among different centres. The main reason forconstituting the ISIORT intraoperative radiotherapy internationalsociety was in fact creating a common and commonly accepted referencepoint issuing protocols and procedures eliminating the local particulardifferences which inevitably set up.

For radiating a particular organ which is exposed due to the surgicalopening, it is not convenient to use X rays which are commonly used forconventional radiotherapy; in fact these are highly penetrative and onceaimed at the area to be treated they involve everything being alongtheir aiming direction, distributing undesired radiation doses also toother organs which are thereby damaged.

Instead, IORT uses a beam of electrons, which are the primary particlesbeing accelerated in order to obtain, after a conversion, the X rays. Infact, the electrons are slightly penetrative ionising radiations andtheir penetration is precisely controlled through the kinetic energythat they are given by the accelerator. A cursory empirical ruleestablishes that the electrons penetrate in a biological tissue for anumber of centimetres equal to their kinetic energy, expressed in MeV,divided in half; hence, a 6 MeV beam shall be completely absorbed withinthe first 3 centimetres of tissue.

Hence, the use of electrons takes away from the danger of damagingorgans beneath the bottom of the tumour bed which is exposed by thesurgeon. Moreover, the electron beams, thanks to the reducedpenetration, are easily shaped and transversely limited, being therebypossible to treat only parts to be radiated, reducing the morbidityinduced by applications of considerable doses such as the ones used inIORT.

The doses normally used in conventional radiotherapy range from 25 to 75Gray, where 1 Gy=1 Joule/1 Kg. These doses are delivered to the patientby means of a series of usually biweekly applications, of 1-2 Gy perapplication. In IORT typical doses range from 10 to 25 Gy, applied onlyonce. It is evident that an error in dosimetry in IORT may be much moredangerous than in classical radiotherapy. Therefore, apparatus dedicatedto IORT has to very precisely detect the dose of electron radiancy.

The shape of beams is obtained by making the electron beam pass withinan applicator made by a tube in plastic material having a wall thicknessof the order of 5-8 millimetres. This thickness is generally sufficientto prevent accelerated particles from spreading outside the beam. Beamshape is generally circular, and rarely polygonal.

When it was initially developed, IORT was performed by moving theanesthetized patient from surgical room to radiotherapy bunker wherethere was the accelerator that was prearranged to emit electrons (theaccelerator is usually an X ray source); the electron beam was appliedthrough applicators in light material capable to shape and limit thebeam itself. In order to eliminate or at least minimise patientmovement, some institutes have built surgical rooms next to or withinthe radiotherapy bunker; in any case these were extremely expensivesolution which have in fact limited the diffusion of IORT.

Hence, a procedure IORT comprises the following steps:

-   -   conventional surgical operation;    -   preparing the patient for transport;    -   transporting the patient;    -   preparing the patient for radiation;    -   treatment with electrons; and    -   ending of the surgical operation.

From an electromagnetic point of view, a machine for radiotherapy isvery similar to a radar transmitter, since it is substantially a veryshort pulse transmitter, pulses having a duration of 1÷5 μsec, and verypowerful, having a power of the order of 2÷5 MW, operating in themicrowave range, with frequency of the order of 3 Ghz corresponding to awavelength λ=10 cm. This microwave pulse enters an acceleratorcomprising a series of cascrewses, which may be resonant or aperiodic,where it generates extremely strong instantaneous electric fields whichcause a beam of charged particles, i.e electrons, to be accelerated dueto electrostatic attraction.

With reference to FIG. 1, a high voltage power supply 1 transforms theline voltage into a continuous voltage, having a value ranging from 9 to18 kV, which charges a system of capacitors wherein the energy needed togenerate a single pulse is stored. Through a suitable switch calledthyratron, a pulse generator 2 transforms the previously stored energyinto a pulse having a short duration, equal to about 1÷5 μsec, and avoltage of the order of 50 kV.

This pulse is applied to a microwave generating thermionic tube 3, saidmagnetron, that transforms it into a train of electromagneticoscillations which are inputted into an accelerating structure 4 forcarrying out the accelarating process of an electron beam.

For a proper operation, all the mentioned devices need auxiliarycircuits and apparatus which provide for proper operation or forstabilizing the whole system depending on the circumstances.

In particular, a synchronizer 5 comprises a set of circuits producingthe pulses that make all the pulse devices of the impulsivi del pulsegenerator 2 coordinatedly work, providing for their proper operationsequence. A tuning control circuit 6 provides for keeping resonancefrequency of magnetron 3 in step with the frequency needed for a properoperation of the accelerator. A vacuum pump 7 maintains a ultra highvacuum level, of the order of 10⁸ hPa (hectoPascal), within theaccelerating structure 4, which is essential in order that theaccelaration process occurs without impediments due to an excessiveimpact of particles with gas molecules within the accelerating structure4. A system 8 for measuring the energy quantity conveyed by the beam andthat is incident on the tissues of the patient allows the emittingprocess to be stopped when the radiated energy quantity reaches a valuewhich is sufficient for the desired therapeutic purposes. Finally, aprocessing computer 9 controls the operations of the machine.

The conventional machines for radiotherapy present some drawbacks.

First of all, as it has been already observed, they do not satisfy therequirement for mobility, also because the apparatus is heavy and bulky.

In fact, in case of immobile machine for radiotherapy, even if it isplaced within a surgical room, yet the patient must be moved in order tobe positioned under it. This implies a complex and difficult logisticorganisation, since the above is a procedure which is extraneous to thenormal conduct of a surgical operation, and a time extension of theanesthesia, further causing a physical stress for the patient.

Moreover, an immobile machine placed in a surgical room may treatpatients at a frequency equal to the one of the surgical operation, thatis, typically, one patient per day for abdominal applications and up tothree per day in case of mammary tumours. However, the time of real useis greatly shorter, since the radiation lasts about one minute and thewhole operation of positioning and subsequent removal of the patientdoes not generally reach 15 minutes. Hence, this results in keepingmostly unused a machine potentially capable of treating an high numberof patients.

Although some mobile machines for radiotherapy have been developed,these have drawbacks due to weight and size and to the need ofcalibration after movements.

Moreover, a machine, either immobile or mobile, is driven onto thepatient to be radiated by a radiotherapy technician skilled in driving,who is, however, not sterile, since he has to handle objects, such asthe remote control, which cannot be sterilised. The machine isconsidered sterile only for the applicator portion fixed thereto. Thepositioning of the machine consists in joining the two portions of theapplicator (one of which is positioned in contact with the surgicalopening of the patient, and the other one is connected to the machine).The technician controlling this action cannot get close to the patient,since he is not sterile, and he is therefore led through vocalinstructions by the (sterile) radiotherapist who is close to thepatient. This procedure is quite dangerous, because the one driving themachine has a very limited sight of the operating zone and there is therisk of hitting or compressing internal organs of the patient which arequite fragile.

Further drawbacks of the known machines for radiotherapy are due to thesystem for diffusing the electron beam.

In fact, the accelerated electron beam leaves the vacuum environment ofthe accelerating structure emerging through a titanium thin foil, whichis interposed in order to keep the vacuum level within the structuresealed. The transverse size, that is the diamater, of the beam at themoment of leaving are of the order of millimetre. Thanks to theelectrostatic repulsion among the electrons and to the diffusion withthe crossed air, the beam opens with an angle depending on the beampower that, at 10 MeV, is of the order of ±10° around the geometricaxis.

As shown in FIG. 2 a, when the energy conveyed by the beam is analysedaccording to relative units by sectioning it with a plane containing theaxis, a Gaussian type distribution is obtained. In order to be usableonto the patient, the beam has instead to have a constant value in thewhole range of application, as shown in FIG. 2 b. For obtaining such atransformation, as shown in FIG. 2 c, the beam is diffused by making itcross a metallic plate 10 having variable thickness and sectioning itwith a light material tube 11, capable to absorb the undesired sideportion of the beam.

However, such beam flattening solution is inadequate for machines forIntraoperative Radiotherapy, since the diffusing plate 10 produces asignificant quantity of braking X rays which permeate the surgical roomenvironment and are difficult to be shielded. This imposes a noticeableshielding which causes high values of the machine weight, making the useof special floors be necessary.

In this regard, the problem of environmental radiation in surgical roomis particularly important.

Besides the already mentioned X radiations due to the diffusing filterscrossing, the environmental radiations which are present duringoperation of an electron accelerator for IORT in surgical room compriseelectron radiations due to electrons leaving the collimator, also knownas secondary electrons, and X radiations generated by the patient, i.e.the electron beam braking radiations due to the fact that the patientbrakes the electron beam absorbing almost its whole energy.

The secondary electron radiations, even being of noticeable number, havea very low energy, estimated in few keV, and generally remained confinedwithin the surgical room. It is therefore sufficient to leave the roomduring radiation.

However, the warning and control procedures are not completely accurate.

The braking X radiations are the most harmful and inevitable. Thepercentage of beam energy which is converted into X rays amounts to 0.3%of the incident energy, the generated X radiations having energy rangingfrom 0 to the energy of the most energetic electron. As shown in FIG. 3,from a geometric point of view the radiation is extremely anisotropic,having a lobe 12 along the running direction of the original electronbeam. The aperture of the lobe 12 is very restricted and at a angle offew degrees deviating from the axis its intensity is halved, while at90° its intensity is reduced to one hundredth of the value on the axis.This remarkable anistotropy makes possible an effective beam,interposing an absorbing mass 13 along the beam axis prolongation so asto prevent the radiation from propagating outside the surgical room. Theabsorbing mass 13 is made of lead slabs. Considering that thedecivalency thickness (that is the thickness of material reducing to onetenth the intensity of the incident beam) at the energies normally usedin IORT is equal to 4 cm, in order to attenuate the incident radiationby a factor ranging from 50 to 1000 the thickness of the absorbing mass13 normally ranges from 6 and 12 centimetres.

However, while in the case of immobile machines for radiotherapy theabsorbing mass 13 is oriented in fixed position with respect to theaccelerator axis, in the case of mobile machines for radiotherapy thecorrect positioning of the absorbing mass 13 is not simple, taking alsointo account the accuracy imposed by the law for the safety of theoperators.

A further drawback present in known machines for radiotherapy is due tothe system for measuring the beam, needed in all the accelerators forradiotherapy in order to determine that the prescribed dose quantity hasbeen really delivered by the machine and to stop delivering.

In fact, transmission ionization chambers are commonly used, which arecrossed by the radiation beam. The chamber is made of two foils ofconductor which is very thin (so as to not attenuate the beam) andspaced 1-2 millimetres and between which a potential difference of somehundreds of volts is maintained. The particles, either electrons orphotons, crossing the space between the foils ionize an amount of airmolecules proportionally to their own kinetic energy and to theirnumber. The ionized molecules are hence attracted by the negativeelectrode while the electrons which are stripped from the externalorbitals migrate to the positive electrode; this current which isgenerated by the passage of the beam is collected by a capacitor and istransformed in a charge amount which is measured by a suitable circuit.Considering that the dose flow is equal to the ratio of pulse dose topulse duration, the ionization chambers remain linear with dose flows ofthe maximum order of about 100 Gy/sec, beyond which the flow generates anumber of electrons and ionized molecules so high that these recombinebefore reaching the ionization chamber electrodes, therefore subtractinga charge amount from the measure. Microscopically this effect istranslated into a progressive desensitization of the chambers up tobeing no more usable.

In case of mobile machines for Intraoperative Radiotherapy, in order tomaintain environmental radiation quantity minimum, the electron beam isnot diffused and must be measured, for reasons of efficient machinearchitecture, directly at the accelerator output, where it still hastransverse size of the order of few millimetres. Since the typical flowof a mobile machine for Intraoperative Radiotherapy is of the order of20,000 Gy/sec, the ionization chambers operate in a very low sensitivityregion that does not allow them to appreciate variations lower than somepoint percent. Considering that the precision limit of clinicaldosimetry is of the order of 2%, it is evident that the transmissionionization chambers are unusable.

The solution which is used in some mobile machines is to employ ascattering filter so as to lower the electron current by a factorranging from 10 to 40 and prevent the transmission chambers from beingaffected by noticeable recombination phenomena. However, such a solutionimplies a very high environmental radiation quantity which imposes theuse of a circular attenuator (a sort of collimator for the diffusion) inheavy material (depleted uranium). The use of such a shielding causesthe radiating head to be heavy and, due to balancing reasons, thispropagates in cascade on the weights of the whole machine.

A further drawback of the known machines for radiotherapy is due to theaccelerating structure.

With reference to FIG. 4, the accelerating structure is composed by aseries of resonant cascrewses 14 coupled among them, which areequivalent to a series of elementary oscillating pure resonant circuits,comprising an inductor L and a capacitor C, coupled between them. Inthis circuit, the resonance frequencies of the elementary cells areadjusted so as to have a 90° phase displacement between the voltages atthe capacitors of two contiguous cells.

With reference to FIG. 5, it may be observed that the acceleratingstructure cascrewses are of two types which alternately follow:accelarating cascrewses 15 and coupling cascrewses 16. In particular,the accelerating cascrewses 15 have a large indictance and a smallcapacitance; their configuration comprises central protrusions 17 whichare the capacitive component, around which it is formed the electricfield that is used to do the acceleration work. Vice versa, the couplingcascrewses 16 have a large capacitance and a small inductance; theirfunction is to transfer the radiofrequency (RF) energy by displacing itsphase of 90°, without participating in the accelerating process. Inorder to accurately adjust the resonance frequencies, the acceleratingstructure comprises tuning micrometer screws 18 which vary the volume ofvariano il volume accelerating and coupling cascrewses 15 and 16.

However, the presence of tuning screws 18 creates a significanttechnological difficulty as far as the vacuum level is concerned.

In fact, within the accelerating structure, the ultrahigh vaccum level,of the order of 10-8 hPa, has to be maintained and in order to obtain itit is necessary a pump continuously operating for the whole operativelife of the accelerator. Hence, each tuning screw 18 has to beaccurately sealed by means of a suitable vacuum brazing. This involvesthe necessity to heat the whole structure up to temperatures of theorder of 500-600° C. These thermal cycles, besides being expensive,since they conspicuously extend the production time of the accelerator,also tend to make the building material get relaxed and, hence, to varyits physical size impairing the precision of tuning.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a machinefor IORT which is easily movable and to be positioned.

It is still an object of the present invention to provide such a machinewhich makes possible, in a reliable, simple and efficient way, toradiate an electron beam drastically reducing the diffusion of X rays,accurately controlling and shielding environmental radiation.

It is a further object of the present invention to provide such amachine which makes possible to very precisely measure the radiationdose.

It is another object of the present invention to provide such a machinewhich is technologically simple to be realised.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be now described, by way of illustration andnot by way of limitation, according to its preferred embodiments, byparticularly referring to the Figures of the enclosed drawings, inwhich:

FIG. 1 shows an electromagnetic block diagram of a machine for IORT;

FIG. 2 a shows the profile of the energy conveyed by the electron beamat the output of an accelerating structure;

FIG. 2 b shows the profile of the energy conveyed by the electron beamwhich is necessary for a IORT treatment;

FIG. 2 c shows an electron beam diffusion system used in the machines ofthe prior art;

FIG. 3 shows a geometrical section draft of radiations generated duringa IORT treatment;

FIG. 4 shows a circuit which is equivalent to an accelerating structure;

FIG. 5 shows a particular of an accelerating structure of the prior art;

FIG. 6 shows a schematic perspective view of the handling means of apreferred embodiment of the machine according to the invention;

FIG. 7 shows a bottom plan view of a preferred embodiment of the machineaccording to the invention;

FIG. 8 shows a schematic side view of the handling means of FIG. 6 in afirst stressing condition;

FIG. 9 shows a schematic side view of the handling means of FIG. 6 in asecond stressing condition;

FIG. 10 shows a schematic side view of the handling means of FIG. 6 in athird stressing condition;

FIG. 11 shows a schematic side view of the handling means of FIG. 6 in afourth stressing condition;

FIG. 12 shows a schematic side view of the handling means of FIG. 6 in afifth stressing condition;

FIG. 13 shows a schematic side view of the handling means of FIG. 6 in asixth stressing condition;

FIG. 14 shows a schematic side view of the handling means of FIG. 6 in aseventh stressing condition;

FIG. 15 shows a schematic side view of the handling means of FIG. 6 inan eighth stressing condition;

FIG. 16 a shows a sectional view of a sensor of the handling means ofFIG. 6 in a first configuration;

FIG. 16 b shows a sectional view of a sensor of the handling means ofFIG. 6 in a second configuration;

FIG. 17 shows an electron beam diffusion system of the machine of FIG.7;

FIG. 18 shows a first particular of the X ray shield of the machine ofFIG. 7;

FIG. 19 shows a second particular of the X ray shield of the machine ofFIG. 7;

FIG. 20 shows a luminous signalling device of the machine of FIG. 7;

FIG. 21 shows a particular of the electron beam total dose measuringsystem of the machine of FIG. 7;

FIG. 22 shows a block diagram of the electron beam total dose measuringsystem of the machine of FIG. 7; and

FIG. 23 shows a particular of the accelerating structure of the machineof FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

In the following of the description same references will be used toindicate alike elements in the Figures.

The machine for IORT according to the invention has a considerablemobility. In particular, the preferred embodiment has a weight lowerthan 400 Kg, eliminating any problem in floor statics and, most of all,in capacity of elevators and vehicles; moreover, it has reduced sizes,having a width of 80 cm, in order to make possible the movement throughthe elevator doors, and a length not larger than 2 metres; still, theturning radius is such to allow the machine to rotate around a verticalaxis placed within the same machine; finally, the preferred embodimentof the machine is provided with autonomy of movement so that it can movewithout necessity to be supplied during transfer.

The machine for IORT according to the invention allows a sterile person,for example the radiotherapist, to directly control movement. Thismobility can be obtained with a “sterile handle”, whose mechanicalstresses caused by the operator's hand are translated into electricalsignals controlling the movements of the machine so as to favour thesame stresses.

With reference to FIG. 6, from a mechanical point of view, the handle ofthe preferred embodiment of the machine is like a prism 19 suspendedfrom ten stress sensors 20, which translate the stress caused by theoperator's hand into electrical signals which, after being interpretedby a control processor, not shown, generate mechanical movements apt tonullify the same stress. In particular, with reference to FIG. 7 theprocessor operates two, respectively right and left, moving engines ofthe machine which act on the two front wheels, respectively right 21 andleft 22, of the machine, and engines for moving the radiating head 23 ofthe machine, from which the electron beam comes out. The sterile handleis placed in correspondence with the radiating head 23. The machinestill comprises two rear wheels, respectively right 24 and left 25,which are idle and pivoting. Preferably, the two driving wheels 21 and22 are provided with a clutch, that may be operated through a suitabletool, which uncouples them from the respective engine and makes themidle; this makes possible a rapid push motion in case of shutdown orfailure. Moreover, the machine is provided with engine supplyingbatteries which make it autonomous during transfers.

Thanks also to the independence of the two driving wheels 21 and 22, theservomechanism formed by the ten sensors 20, the processor, the twomoving engines of the machine and the engines for moving the radiatinghead 23 of the machine allows the machine to have five degrees offreedom:

-   -   rectilinear motion of the whole machine onto a plane,    -   rotational motion of the whole machine onto a plane,    -   vertical translation motion of the radiating head 23,    -   roll motion of the radiating head 23, and    -   pitch motion of the radiating head 23.

The ten sensors 20 form the five bidirectional sensors needed for thelisted five degrees of freedom, apt to measure both the traction stressand the compression stress. For reasons of simplicity and reliability,the preferred embodiment of the machine according to the inventioncomprises, instead of five bidirectional sensors, ten sensors 20 apt toreact only to compression stresses, being much more sturdy and precisethan bidirectional sensors.

The user takes the prism 19 in correspondence of its centre and mayimpress a force in any direction. With reference to FIG. 8, assumingthat the user impress a forward uniform stress, as indicated by thearrow in FIG. 8, the two front sensors, respectively top 20 uF andbottom 20 lF, are stressed, detecting a compression, and give two equalsignals; in particular, in FIG. 8 the stressed sensors are shown ingrey. The control processor of the servomechanism analyses the signalscoming from all the ten sensors 20 and operates the two moving enginesat identical speed so as to impress to the machine a forward movement.Similarly, with reference to FIG. 9, if the user impress a rearwarduniform stress, as indicated by the arrow in FIG. 9, the two rearsensors, respectively top 20 uB and bottom 20 lB, shown in grey, arestressed and give two equal signals that the control processorinterprets for operating the two moving engines at identical speed so asto impress to the machine a left sideways movement. In particular, inthe following of the present description a stress involving only twosensors 20 placed on the same side is indicated as an equally directedstress.

Still with reference to FIG. 6, it is evident that if the equallydirected stress is impressed to two side sensors, alternatively to theright sensors 20 uR and 20 lR or the two left sensors 20 uL and 20 lL,the control processor generates an inverted rotation of the two movingengines (the right engine rotates clockwise and the left one rotatesanticlockwise or vice versa) which is proportional to the stress, thatcauses a rotation around a vertical axis which is central with respectto the segment joining the axis of the two driving wheels.

These movements may be combined in an infinite series of elementarytranslations and rotations, since the control processor continuouslyanalyses the stresses which are impressed to the prism 19 andconsequently modifies the commands sent to the moving engines.

Differently, differential stresses onto the sensors 20 producecorresponding signals that the control processor analyses so as tooperate the engines for moving the radiating head 23 of the machinewhich generate rotations of the radiating head 23, and precisely,depending on which pair of sensors 20 is stressed, roll or pitchrotations. In particular: in the case when the front top sensor 20 uFand the rear bottom sensor 20 lB are stressed, a pitch rotation isgenerated as shown by the arrow of FIG. 10; in the case when the frontbottom sensor 20 lF and the rear top sensor 20 uB are stressed, a pitchrotation is generated which is the opposite of the previous one, asshown by the arrow of FIG. 11; in the case when the right top sensor 20uR and the left bottom sensor 20 lL are stressed, a clockwise rollrotation is generated; finally, in the case when the right bottom sensor20 lR and the left top sensor 20 uL are stressed, an anticlockwise rollrotation is generated.

Also in this case it is possible to have movements which are acombination of pitch rotations and roll rotations, that may befurthermore combined with the previously illustrated movements.

Finally, a stress onto the 20T placed at the top of the prism 19generates a lifting of the radiating head 23, as shown in FIG. 12, whilea stress onto the sensor 20D placed at the base of the prism 19generates a lowering of the radiating head 23, as shown in FIG. 13.

The movements of the servomechanism, above illustrated with reference toFIGS. 8-13, are related to a configuration of the radiating head 23, towhich the handle 19 is integral, placed in vertical position, that is intransport position. The control processor allows the machine to becorrectly moved even when the radiating head 23, and consequently theaxis of the prism 19, has a different orientation and, hence, thedirections toward which the operatore impress in order to obtain acertain movement involve other sensors.

Purely by way of illustration and not by way of limitation, it isassumed that the radiating head is rotated of 45° forward, as shown inFIG. 14. In order to lift it, the operator upward pushes the whole prism19 which transmits the stress, besides the top sensor 20T, also to thetwo front sensors 20 uF and 20 lF, all pointed out in grey in FIG. 14.Similarly, in the limit case (usually not possible) of the radiatinghead 23 and the prism 19 rotated of 90°, in order to lift the head onlythe front sensors 20 uF and 20 lF are stressed, as shown in FIG. 15.

In order to correctly operate the engines for moving the radiating head23 or the whole machine, the control processor performs the followingoperations:

determining the orientation of the prism 19 with respect to a firstCartesian triad which is integral with the machine;

composing, according to the determined orientation of the prism 19, thestresses which are measured by the sensors 20 (each one of which detectsonly the stresses which are orthogonal to it), until a resulting vectorand a resulting torque are obtained with respect to a second Cartesiantriad which is integral with the prism 19;

calculating the projections of the resulting vector and of the resultingtorque onto the first fixed Cartesian triad of the machine, obtainingthe vector of translation of the whole machine, the torque of rotationof the whole machine, the vector of vertical translation of theradiating head 23, the torque of roll rotation of the radiating head 23,and the torque of pitch rotation of the radiating head 23; and

operating the two engines for moving the whole machine and the enginesfor moving the radiating head 23 proportionally to the obtained vectorsand torques.

The stress sensors 20, also known as load cells, suffer for possible,even modest, overloads, because they break at a stress equal to 1.5times their full-scale maximum charge. With reference to FIGS. 16 a and16 b, in order to detect stresses which are proportional to the onesimpressed by the operator, the preferred embodiment of the machineaccording to the invention has a protection of the sensors 20. Inparticular, each sensor 20 is inserted into a mechanical housing 26that, by means of a deformable elastic element 27, such as a spring,limits the accidental maximum stress that can be applied to the sensor20. In particular, FIG. 16 a shows the housing 26 in its not stressedlimit position, while FIG. 16 b shows the housing 26 in its limitposition of maximum stress onto the sensor 20. As shown in FIG. 16 b,the elastic element 27 deforms up to the housing 26 reaches a mechanicalstop, such as a beat with the handle structure, the maximum stressexerted onto the sensor 20 in this case being non larger than thefull-scale of the same sensor.

Moreover, all the electronic, electromagnetic, and mechanical componentsof the machine, which are sensitive to humidity, are enclosed in sealedcompartment, so as to make sterilization of the whole machine inautoclave possible.

In order to make flatt, instead of Gaussian, the energetic profile ofthe diffused electron beam and eliminating the problem of the generationof braking X rays due to a diffusing plate, the machine for IORTaccording to the invention provides that the beam diffusion systemcomprises, as shown in FIG. 17, a divergent magnetic lens 28 fordiffusing the beam. The lens 28 does not produce any radiation and islimited to make the electron trajectories diverge; in particular, a tube11 in light material selects the diffused beam, absorbing the undesiredside portion of it, obtaining the needed uniformity over the range ofapplication, according to the profile shown in FIG. 2 b.

Advantageously, the machine has luminous devices for signalling thecondition of machine on and of beam emission. Moreover, the machine mayfurther be provided with a timer of duration T, preferably equal to 30seconds, still more preferably adjustable, during which an acousticdevice is operated to indicate the requirement of leaving the forbiddenareas before the start of the beam emission. Such signalling devicesfacilitate the delimitation of suitable guard areas which have to beleft only for the short radiating period, usually of lasting 30 to 60seconds, avoiding the use of uncomfortable and bulky mobile shieldswhich uneasily are maintained sterile.

As mentioned with reference to FIG. 3, in order to shield the braking Xradiations generated by the patient, it is necessary to position anabsorbing mass 13, comprising one or more lead, along the the beam axisprolongation.

With reference to FIGS. 18 and 19, the preferred embodiment of themachine according to the invention comprises a shield including a mobilesteel stand 29, preferably provided with lockable wheels 30, to which anabsorbing mass 13 is coupled which is mobile with respect to the stand29 by means of a sliding mechanism 31.

An anchorage dome 32 of a detecting device 33 is integrally coupled tothe centre of the absorbing mass 13, the detecting device 33 beingintegrally coupled to the machine 34, substantially at the same heightof the duomo 32. In particular, the detecting device 33 measures throughtwo potenziometers 35, the azimuth angle and the distance from thecentre of the absorbing mass 13 with respect to the machine 34. Thesedata, together with the elevation, the roll angle and the pitch angle ofthe radiating head, are processed by a processor, preferably the samecontrol processor of the servomechanism of the machine, for univocallydetermining the position of the beam axis on the surface of theabsorbing mass 13.

With reference to FIG. 20, the processor also drives a luminoussignalling device 36 that gives indications to the operator forsignalling the possible needed movements for correctly positioning theshield or the reached attainment of the correct position.

The preferred embodiment of the machine according to the inventionfurther comprises a radiated beam measuring system that, instead of atransmission ionization chamber, which cannot be used for the high doseflows used for IORT, includes an amperometric transformer that measuresthe electron beam current at the output of the titanium window of theaccelerating structure.

The electron beam energy fluency, which may be measured in terms of doseonly after being absorbed by a material, is given by the productV_(accelerating)×I_(beam), where V_(accelerating) is the acceleratingvoltage and I_(beam) is the electron beam current. In the machineaccording to the invention, which comprises a stationary waveaccelerator, the current production is related to the resonance of thecascrewses, like also the creation of the accelerating electric fieldsand, consequently, the voltage V_(accelerating). Hence, assuming theelectron injection constant, an equal variation of kinetic energycorresponds to a small variation ΔI_(beam) of the current I_(beam).Therefore, instead of using a system for measuring the acceleratingvoltage V_(accelerating), the measure of the dose is based on themeasure of the beam current I_(beam), the instantaneous dose having adependency of quadratic type from thisD=K*I_(beam) ²which results linearizeable for small variations ΔI_(beam) that usuallyare observed during the operation around the reference value I_(beam)_(≦) _(Ref), wherein ΔI_(beam)<0.1 I_(beam) _(—) _(Ref), usually plusΔI_(beam)≦0.03 I_(beam) _(—) _(Ref). Therefore, the instantaneous dose Dis obtained through the following linear relation from the measure ofthe beam current I_(beam), i.e. from the variation ΔI_(beam) of this(ΔI_(beam)=I_(beam)−I_(beam) _(—) _(Ref)):D=D ₀ +A*ΔI _(beam)where D₀ and A are experimentally determined in the phase of clinicaldosimetry of the machine, phase which employs dosimetries certifiedindipendent from the energy and from the dose portion, preferablyaccording to Frike dosimetry.

The main advantage is the absolute linearity of the measuring device andthe great stability and independence of the amperometric transformersfrom environmental factors, such as pressure, humidity and temperature.Moreover, with respect to the conventional use of transmissionionization chambers, the use of an amperometric transformer alsoeliminates the need for long and complex calibration measures after themovement of the machine, since an amperometric transformer isinsensitive to vibrations and to acceleration due to transport.

As shown in FIG. 21, from a constructive point of view the measuringsystem comprises a toroidal transformer would on a ferrite toroidal core37 of suitable rating: the primary of such transformer is the electronbeam that, passing through the hole 38 of the torus 37 magneticallylinks with the wounded secondary 39. The short circuit current in thesecondary has a value equal to 1/n of the electron beam currentI_(beam), where n is the number of turns of the secondary 39 which arewounded on the core 37.

With reference to FIG. 22, the current generated on the secondary of thetoroidal transformer 40, which is proportional to the current I_(beam)of the beam to be measured, is inserted in a current buffer circuit 41,which is arranged to increase the impedance of the circuit downstreamthe transformer 40. The output of the buffer 41 supply an integratorcircuit 42 which adds the several current contributions due to theelectron beam pulses, giving at the output a voltage which isproportional to the total energy flow of the emitted electron beam. Suchvoltage is digitalised by an analog/digital converter or ADC 43, whoseoutput is sent to the logical circuits which carry out the comparison ofthe digitalised voltage with the pre-set dose value, in order todetermine the moment when the irradiation process has to be stopped.

Finally, the preferred embodiment of the machine according to theinvention uses, instead of the vacuum brazing, a new seal of the tuningscrew of the accelerating structure which avoid the heating of the wholestructure. In particular, with reference to FIG. 23, each tuning screw18, once inserted into the accelerating structure 44 in the adjustmentfinal position, is covered by a cap 45, preferably in copper, which isdirectly and locally welded to the accelerating structure 44 on eachscrew 18 through an arc welding in controlled atmosphere. In order toprevent the heat from propagating, particular profiles of the structure44 have been studied which avoid this phenomenon. In particular, thestructure 44 presents, in correspondence of each slot for the screws 18,a lip 46 that is welded to the cap 45 favouring heat dissipation; alsothe cap 45 has a protruding frame 47 dissipating heat.

The direct and local electrical arc welding on each screw 18 incontrolled atmosphere shortens of about one third the acceleratormanufacturing time and presents the great advantage of allowing, in caseof loss of seal of a tuning screw 18, the defect to be corrected throughpassing again the electrical arc only onto the defective part, withoutputting at risk the seal of the other screws 18 as, instead, in the casewhen these are brazed with eutectic alloy.

It is evident that the machine according to the invention offers theadvantage of a high mobility, being much lighter and having a reducedbulkiness with respect to the conventional machines. In particular, themachine according to the invention may be easily moved with commonelevators, may autonomously cover paths even of some hundreds of metresinside and outside an hospital, and may be transported with a suitablyequipped vehicle from a clinic to another with no need of recalibration.

The present invention has been described, by way of illustration and notby way of limitation, according to its preferred embodiments, but itshould expressly be understood that those skilled in the art can makeother variations and/or changes, without so departing from the relatedscope of protection, as defined by the following claims.

1. Machine for intraoperative radiation therapy or IORT (Intra OperativeRadio Therapy), comprising a mobile body, provided with at least twodriving wheels (21, 22) and at least an idle wheel (24, 25), eachdriving wheel (21, 22) being operated by a corresponding moving engine,the machine comprising a radiating head (23) connected to the body, aptto emit an electron beam, the machine being characterised in that itfurther comprise handling means (19) which are integral with theradiating head (23), engine means for moving the radiating head (23),apt to impress to the radiating head (23) at least a verticaltranslation motion, said handling means (19) comprising at least threebidirectional sensors (20), apt to measure both a traction stress and acompression stress, each one of which sends to a control processor anelectric signal which is proportional to a measured stress which isorthogonal to the sensor, said control processor operating the movingengines of each of said at least two driving wheels (21, 22) and theengine means for moving the radiating head (23) proportionally to thestresses which are measured by said at least three bidirectional sensors(20).
 2. Machine according to claim 1, characterised in that said enginemeans for moving the radiating head (23) is apt to impress to theradiating head (23) a rotational motion on at least a plane, in thatsaid handling means (19) comprises at least four bidirectional sensors(20), and in that said control processor operates the moving engines ofeach of said at least two driving wheels (21, 22) and the engine meansfor moving the radiating head (23) on the basis of an orientation ofsaid handling means (19).
 3. Machine according to claim 2, characterisedin that said engine means for moving the radiating head (23) is apt toimpress to the radiating head (23) a pitch rotational motion and a rollrotational motion, and in that said handling means (19) comprises atleast five bidirectional sensors (20).
 4. Machine according to claim 3,characterised in that said control processor performs the followingoperations: determining an orientation of the handling means (19) withrespect to a first Cartesian triad which is integral with the body ofthe machine, composing the stresses which are measured by thebidirectional sensors (20), obtaining a resulting vector and a resultingtorque with respect to a second Cartesian triad which is integral withsaid handling means (19), calculating the projections of the resultingvector and of the resulting torque onto the first fixed Cartesian triad,obtaining a vector of translation of the body, a torque of rotation ofthe body, a vector of vertical translation of the radiating head (23), atorque of roll rotation of the radiating head (23), and a torque ofpitch rotation of the radiating head (23); and operating the movingengines of each of said at least two driving wheels (21, 22), so as tolinearly move the body proportionally to said vector of translation ofthe body and to rotate the body proportionally to said torque ofrotation of the body, and operating the engines for moving the radiatinghead (23), so as to vertically translate the radiating head (23)proportionally to said vector of vertical translation of the radiatinghead (23), to impress a roll rotation to the radiating head (23)proportionally to said torque of roll rotation of the radiating head(23), and to impress a pitch rotation proportionally to said torque ofpitch rotation of the radiating head (23).
 5. Machine according to claim1, characterised in that each one of said at least three bidirectionalsensors is formed by a pair of opposed sensors (20), each of which isapt to measure a compression stress which is orthogonal to it. 6.Machine according to claim 5, characterised in that each one of saidcompression stress sensors (20) is inserted in a mechanical housing(26), provided with elastic means (27), mobile between a first notstressed limit position and a second limit position of maximum stressonto the sensor (20), wherein the maximum stress onto the sensor (20) isnot larger than the full scale of this.
 7. Machine according to claim 1,characterised in that each one of said at least two driving wheels (21,22) is provided with a clutch which is apt to uncouple the wheel fromthe respective engine making it idle.
 8. Machine according to claim 1,characterised in that it comprises housing compartments which are sealedagainst external humidity.
 9. Machine according to claim 1,characterised in that it has a weight lower than 400 Kg.
 10. Machineaccording to claim 1, characterised in that it has a width not largerthan 100 cm, preferably not larger than 80 cm, and a length not longerthan 2.5 metres, preferably not longer than 2 metres.
 11. Machineaccording to claim 1, characterised in that it is provided with a systemfor diffusing the electron beam, leaving an accelerating structure (4),which comprises a divergent magnetic lens (28), apt to make thetrajectories of the electrons crossing it diverge.
 12. Machine accordingto claim 1, characterised in that it is provided with timer means apt tooperate an acoustic device for a duration T before the start of theelectron beam emission.
 13. Machine according to claim 12, characterisedin that the duration T is adjustable.
 14. Machine according to claim 1,characterised in that it is provided with a system for measuring thetotal dose of the electron beam, emitted during a IORT treatment for aperiod of duration R, comprising an amperometric transformer, apt tomeasure the instantaneous current I_(beam) of the emitted electron beam,the instantaneous dose D being calculated as a function of saidinstantaneous current I_(beam), the total dose being calculated througha time integration of the instantaneous dose for the treatment period.15. Machine according to claim 14, characterised in that saidinstantaneous dose D is calculated on the basis of a quadraticdependency from said instantaneous current I_(beam): D=K*I_(beam) ². 16.Machine according to claim 14, characterised in that said instantaneousdose D is calculated on the basis of a linear dependency from saidinstantaneous current I_(beam),D=D ₀ +A*ΔI _(beam) where ΔI_(beam)=I_(beam)−I_(beam) _(—) _(Ref)wherein I_(beam) _(—) _(Ref) is a reference value of the instantaneouscurrent of the emitted electron beam, and the coefficients Do and A areexperimentally determined in a phase of clinical dosimetry of themachine.
 17. Machine according to claim 1, characterised in that theelectron beam comes out from an accelerating structure (4) comprisingtuning means (18, 47), placed in corresponding slots of the acceleratingstructure, said tuning means (18, 47) being directly and locally weldedto the accelerating structure onto each of said slots through anelectrical arc welding in controlled atmosphere.
 18. Machine accordingto claim 17, characterised in that the accelerating structure presents,in correspondence of each slot, a profile apt to dissipating heat. 19.Machine according to claim 17, characterised in that said tuning means(18, 47) comprises a tuning screw (18) covered by a cap (45). 20.Process for moving a machine for intraoperative radiation therapy orIORT (Intra Operative Radio Therapy), comprising a mobile body, providedwith at least two driving wheels (21, 22) and at least an idle wheel(24, 25), each driving wheel (21, 22) being operated by a correspondingmoving engine, the machine comprising a radiating head (23) connected tothe body, apt to emit an electron beam, the machine further comprisinghandling means (19) which is integral with the radiating head (23),engine means for moving the radiating head (23) and which is apt toimpress to the radiating head (23) a vertical translation motion, apitch rotational motion and a roll rotational motion, said handlingmeans (19) comprising at least five bidirectional sensors (20), theprocess being characterised in that it comprises the following step:determining an orientation of the handling means (19) with respect to afirst Cartesian triad which is integral with the body of the machine,composing the stresses which are measured by the bidirectional sensors(20), obtaining a resulting vector and a resulting torque with respectto a second Cartesian triad which is integral with said handling means(19), calculating the projections of the resulting vector and of theresulting torque onto the first fixed Cartesian triad, obtaining avector of translation of the body, a torque of rotation of the body, avector of vertical translation of the radiating head (23), a torque ofroll rotation of the radiating head (23), and a torque of pitch rotationof the radiating head (23); and operating the moving engines of each ofsaid at least two driving wheels (21, 22), so as to linearly move thebody proportionally to said vector of translation of the body and torotate the body proportionally to said torque of rotation of the body,and operating the engines for moving the radiating head (23), so as tovertically translate the radiating head (23) proportionally to saidvector of vertical translation of the radiating head (23), to impress aroll rotation to the radiating head (23) proportionally to said torqueof roll rotation of the radiating head (23), and to impress a pitchrotation proportionally to said torque of pitch rotation of theradiating head (23).